Hydraulic fracturing, also known as hydro-fracking or fracking, is used by the petroleum industry to stimulate production of oil or gas from a well. Hydrocarbons such as oil and natural gas can be obtained from subterranean hydrocarbon bearing geological formations by pumping a pressurized fluid into a well to create a fracture in the formation or to enlarge a pre-existing fracture in the formation. In a procedure known as slick water fracturing, polyacrylamide polymers are commonly used to reduce pumping pressure by reducing the frictional drag of the water against the well inner tubular walls, the interface of the well tube and geological formation at the puncture points of the well tube, and the penetrated crevices formed by fracturing. Such fracturing fluids have a high viscosity.
The polymers used in slick water fracturing often persist within the producing formation. The polymer residue can plug the permeability of the rock and hinder recovery of the water used in the fracturing treatment. The polymer residue also combines with heavy oil tar by-products. The resulting polymer/tar residue sludge deposits accumulate in production tubing and equipment. The sludge deposits can form a filter cake at the injector near wellbore, resulting in damage to the injectors, loss of injectivity, and a loss of capacity once the well is put into production. The polymer/tar residue can plug the permeability of the rock and hinder recovery of the water used in the fracturing treatment. In addition, the residue can foul surface equipment such as solids screening equipment. The frequent cleaning needed to remove the accumulated deposits is time-consuming and reduces the efficient recovery of petroleum products.
Strategies to mitigate polymer persistence include the use of oxidizers producing free radicals to break down the viscosity of polyacrylamide in the slick water. However, these approaches were generally developed for the use under conditions of high temperatures and/or acidic environments. Many wells are located in cold climates. Slick water typically has a neutral to alkaline pH. Strategies for removal of wellbore tar incursion have relied generally on mechanical methods, such as increased hydrostatic pressure in the wellbore, or chemical methods, based on solubilizers or dispersants. These approaches typically do not mitigate polymer persistence. There is a continuing need for methods of efficient methods of well cleaning that are effective under field conditions.